Coronaviruses represent a unique group of enveloped RNA viruses with an unusual replication strategy and distinctive structure. These viruses cause significant respiratory disease in humans, and respiratory, enteric, and disseminated disease of animals. Recent studies in this laboratory have demonstrated several unique features of the coronavirus. The two glycoproteins which form the viral envelope may be responsible for many of the distinctive characteristics of coronarvirus infection. The glycoprotein of the peplomers, E2, an N-glycosylated, 180k molecular weight molecule, is cleaved during virus release to yield two 90k species. The significance of this cleavage in determining coronavirus pathogenicity is a matter of great importance. E2 also exhibits temperature-dependent conformation changes at physiological pH, which may account for the unusual thermal lability of coronaviruses. The other glycoprotein, called El, appears to be an O-linked glycoprotein. It has hydrophobic properties and aggregates on boiling in SDS with Beta-mercaptoethanol. El also interacts with the nucleocapsid. The restricted intracellular migration of El may deterine the characteristic intercellular budding sites of coronaviruses. This glycoprotein may serve as a model for the synthesis and processing of O-linked cellular glycoproteins. In order to elucidate coronavirus replication, we will undertake detailed studies of and structure and functional domains of E2 and E1. We will determine the specificity and function of cleavage of E2 by structural analyses, studies with proteases, and analogues of the cleavage site. The antigenic sites on E2 and E1 will be mapped with monoclonal antibodies. We have demonstrated a host glycosaminoglycan associated with the coronavirus envelope. We will analyze the interaction of this species with the virus so that we can determine its biological effects. These studies are expected to provide a foundation for understanding coronavirus replication and pathogenesis, improve techniques for primary isolation if coronaviruses, and produce new reagents for diagnosing coronavirus infections.